The main goal of this research proposal is to provide new knowledge regarding the basic mechanism involved in the degradation of plasma triglyceride-rich lipoproteins. Although adipose tissue and post-heparin plasma lipoprotein lipase(s) are more directly involved in the metabolism of triglyceride-rich lipoproteins, human milk is an abundant source of one of the lipoprotein-lipases, i.e., the C-II-activated lipoprotein-lipase (LPL-II). Since there is a close antigenic relationship between human milk and plasma LPLC-II, the more accessible milk enzyme will be used as a model for studying the chemical, physical, immunologic and functional properties of this group of lipolytic enzymes. The specific aims of this study include: 1) isolation and purification of human milk LPLC-II, 2) determination of physical, chemical and immunologic properties of human milk LPLC-II, 3) studies on the kinetic properties of human milk LPLC-II, 4) development of a method for a concurrent measurement of activities and protein concentrations of post-heparin plasma lipoprotein lipases and triglyceride lipase, and 5) studies on the lipolysis of triglyceride-rich lipoproteins by human milk LPLC-II and the chemical characterization of lipoprotein degradation products. These studies may clarify the role of lipoprotein lipase(s) in the catabolic conversion of triglyceride-rich to triglyceride-poor lipoproteins, provide new information about the pathogenesis of hypertriglyceridemia, and, in general, contribute to a better understanding of lipid transport processes.